The present invention relates generally to systems for handling textile yarn and more specifically to an improved device for unthreading the yarn from a bobbin.
Systems have been proposed for unthreading any type of textile yarn from a fixed bobbin placed on a creel, or a spindle or the like, by pulling the yarn off the end of the bobbin as opposed to unrolling. The yarn which has come from this fixed bobbin is passed through a guide or an eyelet called an "unthreading eyelet" and then is passed onto the treatment station. Throughout the entire operation, the tension applied to the yarn upstream from the unthreading eyelet must be as constant as possible; if not, variations in tension will be produced downstream from the unthreading eyelet and these tend to cause faults, and sometimes even breakage of the yarn.
In such a system for unthreading, the angle, called the "unthreading angle .alpha." formed by the straight line which joins the center of the unthreading eyelet to the opposite edges of the bobbin, must be at least close to, but slightly greater than, a predetermined minimum value. This unthreading angle essentially varies in accordance with (1) the distance between the eyelet and the bobbin, (2) the nature of the yarn treated, (3) the diameter of the winding on the bobbin, (4) the length of the winding, (5) its angle of inclination, (6) the pitch of the yarn on the winding (that is to say its inclination), (7) the coefficient of friction of the yarn against the eyelet, and (8) the rate of unthreading.
In practice, the precise value of the unthreading angle .alpha. is determined by a simple procedure, which will be described later with reference to the drawings. Generally with an increase in the size of the bobbins and the working speed, either the unthreading angle .alpha. decreases or the bulk of the machine increases.